Formula One's rookie drivers have been warned to watch out in qualifying for next week's Monaco Grand Prix amid fears the new knockout format could pose more of a risk than ever.

Qualifying has changed from last year's single lap session, with each driver running alone on track against the clock, to a knockout format.

Former champion Jacques Villeneuve said "Monaco will be hell" when asked about the prospect at last weekend's Spanish Grand Prix, while Australian Mark Webber of Williams said the first session in particular would be very difficult.

"We have literally told a few rookies that if they do back off at all, you really have to look in your mirror after every corner because a car can be on top of you that quickly," said Webber, who finished third last year and whose German team mate Nico Rosberg is one of the new faces on the starting grid.

"As long as people are sensible enough not to have huge speed differences, that's the bit that worries us," he added. "You don't want that.

"We just mentioned the other day with the group of drivers that of all places, Monaco's very important in terms of you actually have nowhere to go if you back off in certain areas and you don't want to be learning about that in qualifying.

"The experienced guys know the score but every so often you get caught out," said Webber.

"Monaco is just so bad, telemetry is bad, you can't see where the cars are really on the track, radio's bad ... but it'll be fine. It makes it interesting."

Apart from Rosberg, who raced in Monaco in GP2, Toro Rosso's American Scott Speed and Super Aguri's French stand-in Franck Montagny will be making their Monaco Grand Prix debuts.

NEW FORMAT

All 22 cars run together in a first 15 minute session, before the slowest six are removed. The quickest 10 who make the cut after a second stint then battle for pole.

While Monaco is the slowest grand prix, drivers roar unsighted through the corners of the tight and twisty streets trusting that the road ahead is clear.

Any driver slowing down after setting a quick lap presents a real hazard to others coming through at speed.

McLaren's Juan Pablo Montoya was sent to the back of the grid last year for causing "a completely avoidable accident" in practice when he dropped his speed from 278kph on the previous lap to a mere 86 on the fast approach to Casino Square.

Rivals accused him of doing it deliberately to get his own back at being impeded on a previous lap, something Montoya denied, but the consequences were nearly catastrophic.

Villeneuve, coming up behind in his Sauber, was unsighted and ploughed into the back of David Coulthard's Red Bull.

The Canadian said afterwards that he and several spectators could have been killed had his car hit Coulthard's rear wheel and taken off.